Trending Science: Very hungry caterpillars a surprise weapon in the fight against waste

The accidental discovery happened when one of the scientific team, Federica Bertocchini, who is also an amateur beekeeper, was removing the wax moth larvae (which in the wild live as parasites in bee colonies) from the honeycombs in her own hives. She temporarily kept the larvae in a typical plastic shopping bag, which then became riddled with holes.

Bertocchini, from the Institute of Biomedicine and Biotechnology of Cantabria (CSIC), Spain, collaborated with colleagues from the University of Cambridge’s Department of Biochemistry to investigate further and undertake a timed experiment. Around a hundred wax worms were exposed to a typical plastic bag from a UK supermarket. Holes started to appear after just 40 minutes, and after 12 hours there was a reduction in plastic mass of 92mg from the bag.

The researchers, publishing their results in the journal ‘Current Biology’, say that the degradation rate is extremely fast compared to other recent discoveries, such as bacteria reported last year to biodegrade some plastics at a rate of just 0.13mg a day. Polyethylene takes between 100 and 400 years to degrade in landfill sites.

‘If a single enzyme is responsible for this chemical process, its reproduction on a large scale using biotechnological methods should be achievable,’ commented Cambridge''s Paolo Bombelli, first author of the study. ‘This discovery could be an important tool for helping to get rid of the polyethylene plastic waste accumulated in landfill sites and oceans.’

Polyethylene is largely used in packaging and accounts for 40 % of the total demand for plastic products across Europe, where up to 38 % of plastic is discarded in landfills. Globally, people use around a trillion plastic bags every year. The challenge is that plastic is highly resistant to breaking down, and even when it does so, smaller pieces choke up sensitive ecosystems without degrading, thus causes significant damage to the natural environment.

Yet nature may provide an answer. The beeswax on which wax worms grow is composed of a highly diverse mixture of lipid compounds: building block molecules of living cells, including fats, oils and some hormones.

The researchers say it is likely that digesting beeswax and polyethylene involves breaking similar types of chemical bonds, although they add that the molecular detail of wax biodegradation requires further investigation. However, to confirm that it wasn’t just the chewing mechanism of the larvae degrading the plastic, the team mashed up some of the worms and smeared them on polyethylene bags, with similar results.

‘The caterpillars are not just eating the plastic without modifying its chemical make-up. We showed that the polymer chains in polyethylene plastic are actually broken by the wax worms,’ said Bombelli. ‘The caterpillar produces something that breaks the chemical bond, perhaps in its salivary glands or symbiotic bacteria in its gut. The next steps for us will be to try and identify the molecular processes in this reaction and see if we can isolate the enzyme responsible.’

The team are now planning to implement their findings into a viable method to get rid of plastic waste and the research team have since patented the discovery.

‘However, we should not feel justified to dump polyethylene deliberately in our environment just because we now know how to bio-degrade it,’ Bertocchini concludes.